The electronics industry has placed increasing demands on substrates for dissipating larger and larger quantities of power. Similarly, applications involving domestic appliances and industrial instrumentation have begun to explore the advantages of size, weight and cost reduction for which the electronic industry has been the proving grounds.
Dielectric coated metals, with their excellent mechanical and thermal properties and their low cost potential, are a material of choice in a growing number of applications. These include under-the-hood automotive circuitry, surface-mounted components, hybrid circuit boards, multi-chip modules, and heaters, heat sensors and heat regulators in industrial and domestic applications. However, wet chemical processing requirements, temperature limitations, difficult fabrication processes and high cost associated with conventional aluminum and steel core (porcelain enamel) substrate approaches have restricted their usage in this regard.
Particularly in the area of heaters, it has been proposed to make such apparatus by, e.g., making substrates for printed circuits and then applying circuit tracks on the substrate, such as by screen printing, and then firing the printed material onto the substrate. The printed material may be either highly conductive, thus forming a printed conductor or may be in the form of resistive or dielectric layers. The material is typically applied in the form of a paste, and the substrate may be as noted above. Particularly advantageous are such substrates made of enamel steel. However, enamel steel substrates have been used typically only for special applications, due to the typically low softening temperature of the enamel, which limits firing temperatures of the respective pastes to below about 650.degree. C., and due to their limited corrosion resistance.
Accordingly, it has been desired to provide a substrate suitable for use with printed circuits, which have robust mechanical properties and excellent corrosion resistance to make them attractive in a variety of domestic appliance applications. In particular, low profile heaters prepared by screen printing thick film circuitry on such substrates have been desired.